If you tax something, you will get less of it, and if you subsidise something, you will get more of it. A policy like this would lead to more students selecting majors with poor career prospects, and fewer students selecting ones that will enable them to find lucrative employment upon graduation. Also, the subsidies will have to change every year: as the students shift from the higher-priced STEM fields into lower-priced fields, there will be fewer STEM students to subsidise the liberal arts, which will necessitate a higher price-per-student surcharge on STEM. It’s like the insurance death spiral, except that it’s an entirely self-inflicted problem. It’s “helping” the higher education bubble the same way that my cat “helps” me work by sitting on my laptop.

Better solution: introduce these students, who are allegedly there to be educated, to the concept of “debt to income ratio”. Then explain it in terms of average starting salary for various majors. Let them choose accordingly. Also introduce them to this wonderful concept called a “double major”, in which they indulge their interest in Ancient Greece while earning a degree in chemical engineering.